Automatic fire detection - detector circuits

Question 1

The function of the detector circuit in an automatic
detection system is to transmit the signal given
by the activated detector head (or manual call
point) to centrally situated control and indicating
equipment from which the alarm is raised. In practice
these processes occur simultaneously.
Basically, there are two types of detector circuit

Answer 1

Open circuit

Closed circuit

Question 2

Describe the Open circuit

Answer 2

Detectors or call points wired in parallel
Regarded as switches in off position
No current running thru in stand by
Operation close contacts, completes circuit and raises alarm
NOT self monitoring

Question 3

Describe a Closed circuit

Answer 3

Modern systems are closed
Series
Once a detector or call point operates the detector circuit is broken, interrupting current flow to the relay
main advantage of this type of circuit is that
the continuous current on standby makes it partly self-monitoring

Question 4

Discuss power supplies to an automatic fire detection system

Answer 4

Mains
Battery back up at least 24hrs
transfer of power should be automatic
transfer should not affect system